This application relates generally to an apparatus and method for exciting a servo control system in a disc drive with a feed-forward signal with a constrained maximum derivative and more particularly to a method and apparatus for exciting a servo control system with a sinusoidal feed-forward signal.
The storage medium for a disc drive is a flat, circular disc capable of retaining localized magnetic fields. The data stored upon the disc find physical representation through these localized magnetic fields. The data are arranged on the disc in concentric, circular paths known as tracks. The localized magnetic fields can be detected by a magnetically sensitive head when the field is brought in close proximity to the head.
The head is mounted upon an actuator arm that is rotated by a servomotor. Accordingly, the track position of the head is controlled by the servomotor. When the head needs to access a different track, the actuator arm is rotated, bringing the head to the desired track position. The process of moving the head to a new track, referred to as seeking, includes an acceleration and a deceleration phase, and the period during which seeking occurs is known as the access time.
In some disc drives, seek operations are controlled by a feedback loop, which may be excited by a feed-forward control signal. In such a disc drive, the control process typically works as follows. During the acceleration phase of the seek operation, a feed-forward signal is used to excite the servo system, resulting in the head being accelerated along a circular arc. While the head is experiencing acceleration, its velocity and position are periodically measured, and these measurements are compared against desired or xe2x80x9ctargetxe2x80x9d velocity and position values. The differences between the measured values and the target values are subsequently used to adjust a current that drives the servomotor.
During deceleration, a negative feed-forward signal is used to excite the servo system, resulting in the head being decelerated. Once again, while the head is decelerated, its velocity and position are periodically measured, and these measurements are compared against target velocity and position values. Again, the differences between the measured values and the target values are used to subsequently adjust the current that drives the servomotor.
One particular drawback of the above-described seek operation is that it results in a trade off between the seek performance of a disc drive and its acoustic qualities. Reducing access times results in a noisier disc drive, and vice versa. This trade-off is viewed differently by different sorts of disc drive users. For example, within the realm of consumer electronics, most users are willing to sacrifice seek performance in favor of acoustic silence. On the other hand, other customers may prefer enhanced seek performance, even at the expense of disc drive acoustics. As a consequence, some disc drives permit an xe2x80x9cacoustic factorxe2x80x9d to be set. The acoustic factor allows the balance between seek performance and drive acoustics to be selected.
Several attempts have been made to adjust the acoustic quality of a disc drive based upon an xe2x80x9cacoustic factor.xe2x80x9d These attempts have typically shared one or more of the following shortcomings: the noise control technique is ineffective for long seeks; the noise control technique is ineffective for short seeks; acoustic noise is generated during periods of transition between acceleration and deceleration of the head; or, the noise control technique dramatically affects drive performance.
As is made evident from the foregoing discussion, there exists a need for a scheme by which an acoustic factor may be used to determine the tradeoff between seek performance and drive acoustics. A successful scheme will be implementable for short seeks, and will require little additional hardware.
Against this backdrop the present embodiments have been developed. A method of controlling acoustic noise generated by a seek operation in a disc drive may be realized by using a feedback control system to control the seek operation. The feedback control system is excited by a feed-forward signal during execution of the seek operation. Next, an acoustic factor, which defines a seek operation noise level, is selected. Thereafter, the feed-forward signal is generated based, at least in part, upon the selected acoustic factor. (The feed-forward signal has a first derivative having a maximum value.) The selected acoustic factor is used to select the maximum value of the first derivative of the feed-forward signal.
According to another embodiment, a disc drive may include a magnetically encodable disc for storing data on data tracks written on the disc. Further, it may include a magnetically sensitive transducer for reading data from the disc. The magnetically sensitive transducer is carried by an actuator arm that moves the transducer between data tracks. Also, a motor is attached to the actuator arm for propelling the actuator arm when driven with an electrical current. Finally, a microprocessor programmed to execute a feedback control loop to control a seek operation. The feedback control loop is driven by a feed-forward numeric sequence during execution of the seek operation. The feedback control loop has a numeric output that is converted into the electrical current that drives the servo motor, thereby propelling the actuator arm. The feed-forward numeric sequence is generated, based at least in part upon an acoustic factor, defining a noise level of the seek operation. (The feed-forward numeric sequence has a first derivative having a maximum value.) The acoustic factor determines the maximum value of the first derivative of the feed-forward numeric sequence.
According to another embodiment, a disc drive includes a servomotor for propelling an actuator arm during a seek operation. The disc drive also includes a means for determining a noise level of a seek operation, based upon an acoustic factor limiting a derivative of a feed-forward control signal.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.